Surface wave omnidirectional antenna



Jan. 12, 1960 R. s. ELLIOTT SURFACE WAVE ONNIDIRECTIONAL ANTENNA Filed001;. 8, 1954 United States Patent SURFACE WAVE oMNIDIRECTIoNAL ANTENNARobert Stratman Elliott, Pacific Palisades, Calif., assignor to HughesAircraft Company, Culver City, Calif., a corporation of DelawareApplication October 8, 1954, Serial No. 461,261

6 Claims. (Cl. 343-781) This invention relates to microwaveomnidirectional antennas, and more particularly to omnidirectionalantennas of the end-lire type capable of transmitting and receiving amicrowave signal of any desired polarization.

symmetrically excited end-fire omnidirectional antennas heretofore knownare capable of transmitting and receiving microwave signals Vof only onepolarization. An example of such antennas is the symmetrically excitedannular corrugated-surface antenna, which is described in the article,An Annular Corrugated-Surface Antenna, by E. M. T. Jones, Proceedings ofthe I.R.E., Volume 40, Number 6, June 1952. This antenna establishes amajor lobe at the periphery of the corrugated surface, such lobe beingdirected slightly above the plane of the antenna an polarized in adirection perpendicular to the antenna surface. The corrugations act asa trap for the microwave energy for one direction of polarization only.In other words, such an antenna being polarization sensitive requiresspacial orientation with respect to the reception of signals and alsowill suffer varying losses of sensitivity if the echo pulse changes itsdirection of polarization due to reliection and/ or transmission.

It is an object of this invention to obtain an omnidirectional antennacapable of'being symmetrically excited to receive and transmit microwavebeams of any desired polarization.

It is a further object of this invention to provide an end-firevomnidirectional antenna with which a major lobe can be directed in,above or below the plane of the antenna.

It is still a further object of this invention to provide anomnidirectional antenna of the end-lire type which can be symmetricallyexcited, is iiush mounted, and simple in design.

One embodiment of the antenna of this invention is a surface ofrevolution which is connected at its center to a cylindrical waveguideby way of a feed. Any waves which can be excited in the cylindricalwaveguide such as E or H modes of any order are suitable fortransmission or reception. These Waves are trapped or confined in adielectric film deposited on the antenna Which extending from inside thefeed covers the whole surface of revolution. Above the feed andsymmetrically located with respect to the curved surface is a concaveconoid cap which acts as a reliector and whose function is to facilitatethe launching of a surface wave in the dielectric lilm. After theelectromagnetic waves leave the central waveguide or feed, they emergeas surface waves guided equally in all directions by the dielectric cladsurface. The radiation pattern is end-fired and omnidirectional in aplane transverse to the axis of symmetry of the antenna. The directionof the main lobe can be directed in, above, or below the plane of theantenna by providing the surface of revolution with a suitablecurvature.

The novel features which are believed to be characteristic of theinvention, both as to its organization and method of operation, togetherwith further objects and ICC advantages thereof, will be betterunderstood from the following description considered in connection withthe accompanying drawing, in which an embodiment of the invention isillustrated by way of example. The scope of the invention is pointed outin the appended claims. Referring to the drawing, which is made part ofthis specification.

Fig. l is a perspective view of an antenna in accordance with thisinvention; and

Fig. 2 is a sectional View taken along line 2--2 of Fig. l.

Referring to Figs-l and 2, one example of an omnidirectional antenna 'inaccordance with this invention includes a portion which is a symmetricalsurface of revolution 10 which flares outward from the upper portion ofa neck member 12 of circular cross section. Neck 12 is adapted at itslower end to be fixed, as by a seat 14 or other connection means, to oneend of a standard circular waveguide 16. Although the surface ofrevolution 10 is illustrated as having a parabolic cross section, itwill be evident that surfaces of various cross sections-circular,hyperbolic, or even straight lineswill be suitable. The upper part ofthe surface of revolution 10 is covered with a thin dielectric lilm orlayer 18 which extends well into the neck 12 of the surface ofrevolution. The dielectric is provided with a taper 20 near the edge ofthe surface of revolution 10. The main purpose of the taper is toimprove the electrical match from the antenna to free space; the degreeof taper is not critical. Above the neck 12 and concentric with it is adellector 22 which has the shape of a concave conoid with its vertexfacing towards the neck 12. The detiector 22 can be supported in anyarbitrary fashion as, for instance, by means of some struts 24 and 24.

The function ofthe invention is as follows: Electro magnetic waves arefed into the waveguide 16. These waves may be polarized in any desiredmanner. As the electromagnetic waves enter the neck 12, they arecaptured by or trapped in the dielectric film 18 and guided through film18 along the surface of revolution 10.

The waves emerge or are launched from the dielectric at the tapered end20 to be freely radiated into space. The deflector 22 serves tointercept any small fraction of the energy not effectively captured bythe film 18 and to deect it onto the film, thereby insuring thatsubstantially all the energy will be trapped in and guided through film18.

The antenna described in this invention, not being polarizationsensitive, is suitable for transmitting as well as receiving ofmicrowave signals of all polarization. Its band width is determinedsolely by the central waveguide 16. The band width of the antennatherefore stretches from a low end, at which cutoff in the feedingwaveguide occurs, to a high end at which the feeding waveguide isexcited to the next higher mode of propagation.

The antenna described above is a preferred embodiment of this inventionand has a large number of modifications. First, the surface ofrevolution 10 can be of any cross section so as to obtain a radiationpattern having the desired characteristics of a directed main lobe and alow side lobe level. Second, the beacon antenna instead of being asurface of revolution may only comprise a section of the surface ofrevolution, that is a sector anywhere between 0 and 360. Thirdly, sincethe main part of this invention comprises the utilization of adielectric clad metal conducting surface to capture electromagneticwaves and then launch them into space, another modification may beenvisioned by providing the end of a waveguide with a tongue orlaunching platform comprising a dielectric coated conductor. The sameprinciple that made possible the omnidirectional antenna will apply tothis and similar antennas, namely, to utilization of a dielectriccoating to generate a surface wave from a free space wave which can beguided over metallic surfaces and conveniently launched again as a freespace wave.

What is claimed is:

1. An omnidirectional surface wave antenna comprising a hollow circularwaveguide adapted to propagate electromagnetic waves through itsinterior, a radiating element aixed t0 said waveguide having an externalsurface defining a surface of revolution about the centerline of saidwaveguide, non-polarization sensitive means juxtaposed with said surfaceof said element and extending into the interior of said waveguide toconfine and guide electromagnetic waves adjacent thereto over saidsurface of said element, a deflector, said deflector having asubstantially concave conoidal shape, the vertex of said deector beingdisposed to face said waveguide, and means for connecting said deiiectorto said surface.

2. An antenna as defined in claim 1, where the means juxtaposed withsaid surface is a layer of dielectric material.

3. A surface wave omnidirectional antenna comprising a surface ofrevolution with an opening in its center, said surface having acylindrical neck which registers with said opening, a dielectric lm,said film being deposited on said surface, said dielectric lm taperingnear the extremity of said surface to provide a match to free space,said dielectric extending into said neck, a deflector, said detiectorhaving substantially the shape of a concave conoid and being supportedabove said neck with its vertex facing said neck.

4. A surface wave omnidirectional antenna comprising a surface ofrevolution having a substantially parabolic cross section with anopening in its center, said surface having a cylindrical neck whichregisters with said opening, said neck extending in the direction of thefocal point of said surface, a dielectric lm, said film being depositedon the surface of said surface of revolution facing away from the focalpoint, said dielectric extending into said neck, a deliector, saiddeflector substantially having the shape of a concave conoid and beingsupported above said neck with its vertex facing said neck.

5. An antenna comprising' a hollow waveguide adapted to propagateelectromagnetic waves through its interior; a radiating element affixedto said waveguide and having an external surface, said external surfacedefining a surface of revolution of parabolic cross-section about saidwaveguide; non-polarization sensitive means juxtaposed with said surfaceof said element and extending into the interior of said waveguide toconfine and guide electromagnetic waves adjacent thereto over saidsurface of said element, a detiector, said deflector having asubstantially concave conoidal shape, the vertex of said deflectorbeing` .iisposed to face said guide; and means for connecting saiddeector to said surface.

6. An omnidirectional surface wave antenna for the interchange ofelectromagnetic energy between a waveguide and surrounding space, saidantenna comprising a hollow waveguide for propagating electromagneticwaves through its interior and having a centerline therein, a radiatingelement defining a surface of revolution about the centerline axed tosaid waveguide and having an external surface, at least a portion ofwhich extends in a radially outward direction with respect to thecenterline, and a nonpolarization sensitive layer of dielectric materialdisposed on the surface of the radiating element and extending into theinterior of the waveguide, the layer being tapered at itscircumferential extremity to provide a free space match and confiningenergy adjacent to the external surface of the radiating element forproviding an interchange of energy between said waveguide andsurrounding space.

References Cited in the file of this patent UNITED STATES PATENTS2,416,698 King Mar. 4, 1947 2,433,368 Johnson et al Dec. 30, 19472,588,610 Boothroyd Mar. 11, 1952 2,685,068 Goubau July 27, 19542,688,732 Kock Sept. 7, 1954 2,783,467 Gutton et al Feb. 26, 1957FOREIGN PATENTS 685,073 Great Britain Dec. 31, 1952

